Fischer FSS18V 400 BL Replacement Battery 18V 6000mAh Li-ion

Fischer FSS18V 400 BL Series 18V Li-ion 6.0Ah Replacement Battery

This is an 18V 6000mAh Li-ion replacement battery pack for the Fischer FSS18V 400 BL cordless drill/driver range. It fits the FSS18V 400 BL Set 1 through Set 4 and additional models in the same 18V platform. Voltage and cell count match the original pack specification.

• FSS18V 400 BL platform fit: The Set 1 through Set 4 variants share the same 18V battery rail, connector housing, and BMS handshake protocol. One pack works across all four sets because Fischer kept the electrical interface consistent across this tool family.
• Bench tested on actual hardware: We ran this pack through charge and discharge cycles on an 18V platform and monitored BMS response during simulated motor-start inrush. The protection circuit engaged correctly at overcurrent thresholds and recovered without manual reset.
• Motor load conditioning on first use: On first use, run the drill at half load for two cycles before applying maximum torque. This lets the BMS profile the motor’s inrush current draw and set accurate overcurrent protection thresholds before you hit heavy fastening work.

BMS cutoff on trigger pull during motor-start inrush surge

The FSS18V 400 BL brushless motor pulls a sharp current spike the instant the trigger engages. If the BMS has no inrush profile stored common with a new or freshly charged replacement pack it may read that spike as a fault and cut output. This is not a defective battery. Run two half-load cycles first to let the BMS log normal inrush values, then move to full torque applications. After conditioning, the cutoff threshold adjusts and trigger-pull trips stop.

Charger not recognising the new pack after storage

Replacement packs shipped from storage sometimes sit below the charger’s acceptance voltage window typically under 12V on an 18V nominal pack. The charger sees a voltage it doesn’t recognise as safe to charge and refuses to start, often blinking red or showing no response. To recover, briefly connect the pack to a compatible charger that supports recovery mode, or use a lab charger to trickle the cells up to around 1415V. Once above the acceptance threshold, the standard charger takes over normally.